1. Technical Field
The present invention, involving bookbinding apparatuses that bind a spine endface of sheet blocks having been collated into bundles and that finish the sheet bundles into booklets, relates to improvements in bookbinding apparatuses that aligningly stack into bundles sheets onto which images have been formed by, for example, a device such as an imaging apparatus, bind the sheets together into booklets, and trim the booklets' open edges true.
2. Description of the Related Art
Generally, this type of bookbinding apparatus is broadly known as a finishing device that collates into bundles sheets conveyed out from an imaging apparatus or similar source, and that bookbinding-processes the bundle by such operations as adhesive-binding, staple-binding, or adhesive-tape binding the bundle's spine edge. Furthermore, apparatuses furnished with a trimming unit that trims true the open edges of a sheet bundle (booklet bundle) having in this way been binding-processed, as well as apparatuses furnished with a sheet-folding unit, upstream of the sheet stacking tray where sheets are collated into bundle form, that folds sheets in half, in thirds, etc. are also known.
For example, Japanese Unexamined Pat. App. Pub. No. 2005-335262 discloses a bookbinding apparatus wherein sheets onto which images have been formed in an image-forming apparatus are conveyed to the bookbinding apparatus, and in the bookbinding apparatus the sheets are collated and stacked, an adhesive paste is applied to the endface of the spine portion of the sheet bundles, and the sheet bundles are encased with and bound into a cover sheet. The cover-sheet bound bundles are then spine-creased to post-process them into booklet form, and the sheet bundles now made into booklets are finished by trimming true their head/tail portions and fore-edge portions.
In another example, Japanese Unexamined Pat. App. Pub. No. 2006-076779 discloses a post-processing device that in a folding unit folds in half or in thirds sheets onto which images have been formed in an image-forming apparatus, collates the sheets into a stack and staples the stack closed. Therein, proposed are both single-folding, whereby a sheet is folded substantially in half over on itself, as well as Z-folding, whereby in divisions into thirds a sheet is folded inward and then is folded outward back onto itself. It is to be noted that for the sheet-folding device of this reference a trimming-cut configuration that trims true the open edges of sheets having been staple-bound is neither disclosed nor suggested.
As described above, for example, publications such as the foregoing JP 2005-335262 do propose bookbinding devices that collate into bundles (collating/stacking) sheets onto which images have been formed, bind a cover sheet to the spine-portion edge of the sheet bundles (spine-binding process), and then trim true the open edges of the encased bundle (trimming cut). Meanwhile, as bookbinding machines different from this sort of device, publications such as the foregoing JP 2006-076779 do propose bookbinding devices that fold sheets, conveyed out from an image-forming apparatus, in half or in thirds as needed (folding process), collate and stack the sheets (collating/stacking), and bind them together along the edge of the spine portion (spine-binding process).
Against this backdrop, the present inventors attempted the provision, in an image-forming system—like that of the foregoing JP 2005-335262—that collates sheets into bundles and encases the bundles into cover sheets to form booklets, of a device that folds collated sheets in half or thirds, processing them into booklets, and then trims true the open edges (head/tail portions and fore-edge portions). In doing so, however, they came up against the difficulty that in trimming the fore-edge true, the pleat-edge of sheets that had been folded would get sliced.
This slicing of folded sheets is caused by the fact that when trimming the edges of sheet having been formed into a booklet, the folded sheets are trimmed at the same time. A trimming cut on post-bookbinding sheets trims true, by slicing a predetermined amount off, the open edges of book-bound sheets, with as a reference either the sheet edges of the bound inner leaves having been encased into a cover sheet, or the cover sheet itself, whichever is shorter. To solve the fold-slicing problem, the pleat in a folded sheet presumably could be prepositioned in a location where it will not be trimmed off.
Nevertheless, when a sheet bundle is encased in a cover sheet and bound into a booklet, the fore-edge of the cover sheet will be indeterminate if the thickness of the sheet bundle (thickness when covered) is not preestablished. That is, the length from the spine-closure edge to the fore-edge of the cover sheet will differ depending on the sheet-bundle thickness (fore-edge length={cover-sheet size−bundle thickness}/2). Yet the fact that the thickness of a sheet bundle is detected at the stage where the sheets have been collated and stacked into a bundle on the stacking tray means that the final sheet bundle thickness when the sheets (for example the first sheet) have been fold-processed cannot be differentiated. Consequently, in instances where a folded sheet is mixed into a sheet bundle made into a booklet, trim-finishing the booklet after the bookbinding process invites the problems discussed above.